The present invention relates to a linear motor to and a method of manufacture thereof; and more particularly, the invention relates to a linear motor that is provided with an armature on which a coil is to be wound and magnetic poles with pairs of opposing upper and lower magnetic pole teeth, which are arranged alternately.
It has been known conventionally that, if the magnetic field of a linear motor is generated by a permanent magnet, high thrust can be attained with a compact construction. Thus, various constructions have been proposed for a linear motor.
Japanese Application Patent Laid-Open Publication No. SHO 63-310361 discloses a linear pulse motor that can be manufactured at a lower cost by means of a simplified lead treatment. While details of this motor are described in the Publication, a brief description of the construction of the linear motor follows with reference to FIG. 12.
Inside a straight armature 3 having a U-shaped section, two yokes are fixed in parallel, which also have a U-shaped section, and a coil 4 is wound longitudinally on the bottom of each yoke. Each yoke is equipped with two magnetic poles standing upright. A magnetic pole plate is fixed on the top of each magnetic pole, where magnetic pole teeth 20 protrude at an equal interval toward the other magnetic pole plate, thus alternating the magnetic pole teeth 20 and forming a crow pole type magnetic pole surface. A needle 6, which is so held as to be able to move along the longitudinal direction of the armature 3, is equipped with two sets of permanent magnets 7 in parallel with each other so as to face the magnetic pole surface through an air gap, and the permanent magnets 7 are so magnetized that the polarity alternates at the same interval as the protruding teeth of the magnetic pole plate. With this construction, when a two-phase sine wave current with 90-degree phase shift is supplied to the coil 4 wound on each yoke, the needle 6 moves on the armature 3 along the longitudinal direction in response to the well-known linear motor principle.
According to the prior art, while a linear motor can be manufactured at a lower cost by means of a simplified construction and a simplified lead treatment, it involves the following problems. That is, because the two magnetic poles and magnetic pole plates provided for the armature 3 are constructed as explained above, the magnetic flux leakage through the gaps between the alternating magnetic pole teeth 20 protruding from the top of the two magnetic poles is large as a whole. As a result, the thrust of the motor is lower as compared to the exciting current. In addition, since a magnetic attraction force acts between the armature 3 and the needle 6 in one way, a greater burden is imposed on the support mechanism of the needle 6, and, consequently, a strain is caused in the construction, resulting in various problems.